Logging in

Logging in

Before you can do much with a UNIX® system, you need to log in to it. As this may be a new concept for many users, this section briefly explains the need for logging in, how to log in, and how to log out. Note: You will hear various terms used to describe logging in: others say ‘logging on’, or ‘signing in/on’. They’re just different terms for the same thing.

Why the need to ‘log in’?

Many computers that you may have used before are single-user machines. As the name implies, only one user can use the computer at a time. You sit at the computer, do your work, and when you’ve finished, either someone else uses it, or you switch it off.

UNIX is a multi-user operating system. It can have any number of users all using it at once. To prevent this from causing chaos, each user has their own identification, called a ‘user name’ or ‘user ID’. This identifies them to the system. It is allocated by a system administrator, and is often made up of the user’s surname and first initial, such as ‘smithj’ or ‘jsmith’.

Each user has their own ‘space’ within the system. For instance, they have their own area of disk space to use for storing files.

The process of ‘logging in’ is simply a way of saying to the operating system, “I am here, and I want to use the computer”. It identifies you to the system, so that you may have access to your files, but not other peoples’ files. To prevent other users from using your user ID, each user ID also has a password. Only the owner of the user ID should know the password. The system will ask you for the password, and if it is incorrect, you will be denied access to the system. For reference, see Choosing a Password.

How?

Before you log in, the system will only give you one choice: to log in. You cannot perform any other useful tasks on the system before you have done so. Before you log in, the system will display a prompt, which may give you details such as the machine name, and which will prompt you for your user ID. It will look something like what follows below:

london-pro v11.01

login:

In that example, ‘london-pro’ is the name of an imaginary UNIX system. v11.01 is the version number of this system. All login prompts are different, but yours will probably bear some resemblance to this. The important point is that we are being prompted for our user ID. We will now enter our user ID, which we’ll assume is ‘smithj’, and hit ‘RETURN’ or ‘ENTER’ (we’ll assume you hit ‘RETURN’ or ‘ENTER’ after every command, and we won’t mention it again!)

london-pro v11.01

login: smithj

(Throughout this tutorial, text that the user enters is in bold, UNIX prompts and responses are not. On your screen, the text you enter will probably not be bold.)

Assuming that this user ID has a password (and it should!), the system will prompt you for it now. The screen will look something like this:

london-pro v11.01

login: smithj

password:

You may now enter your password. Note that something unusual will happen here: when you enter your password, it will not be displayed on the screen. This is to prevent other users, who may be watching your screen, from seeing it. So even after you’ve typed it, the screen will still appear the same:

london-pro v11.01

login: smithj

password:

After you hit return, one of two things will happen. If you got the password wrong, you will get another go:

london-pro v11.01

login: smithj

password:

Incorrect login

london-pro v11.01

login:

When you get the password correct, you will be logged in to the system. This will cause some text to be displayed on your screen. The exact text is different on each system, and usually includes all manner of copyright messages, restricted rights legends, version numbers, etc. Finally, there may be a welcome message of some sort. An example is shown below:

london-pro v11.01

login: smithj

password:

Copyright 1986-2000 SomeVendor

This system is intended for the use

of employees of SomeCompany.

The date is 2001-01-04 11:34:11am

Welcome to the London Production system.

$

In reality, your system may display more text than this, and the details will be different, but the overall idea will be similar.